In CT X-ray imaging of a patient, X-rays are used to image internal structure and features of a region of the person's body. The imaging is performed by a CT-imaging system, hereinafter referred to as a “CT-scanner” that images internal structure and features of a plurality of contiguous relatively thin planar slices of the body region using X-rays.
The CT-scanner generally comprises an X-ray source that provides a planar, fan-shaped X-ray beam and an array of closely spaced X-ray detectors that are substantially coplanar with the fan beam and face the X-ray source. The X-ray source and array of detectors are mounted in a gantry so that a person being imaged with the CT-scanner, generally lying on an appropriate support couch, can be positioned within the gantry between the X-ray source and the array of detectors. The gantry and couch are moveable relative to each other so that the X-ray source and detector array can be positioned axially at desired locations along the patient's body.
The gantry comprises a stationary structure referred to as a stator and a rotary element, referred to as a rotor, which is mounted to the stator so that the rotor is rotatable about the axial direction. In third generation CT-scanners the X-ray source and detectors are mounted to the rotor. In fourth generation CT-scanners the detectors are mounted to the stator and form a non-rotating circular array. Angular position of the rotor about the axial direction is controllable so that the X-ray source can be positioned at desired angles, referred to as “view angles”, around the patient's body.
To image a slice in a region of a patient's body, the X-ray source is positioned at the axial position of the slice and the X-ray source is rotated around the slice to illuminate the slice with X-rays from a plurality of different view angles. At each view angle, detectors in the array of detectors generate signals responsive to intensity of X-rays from the source that pass through the slice. The signals are processed to determine amounts by which X-rays from the X-ray source are attenuated over various path lengths through the slice that the X-rays traverse in passing though the slice from the X-ray source to the detectors. The amounts by which the X-rays are attenuated are used to determine an X-ray absorption coefficient for material in the slice as a function of position in the slice. The absorption coefficient is used to generate an image of the slice and identify composition and density of tissue in the slice.
The X-ray detectors comprised in a detector array of CT-scanner are generally packaged in a plurality of modules, hereinafter referred to as “CT detector-modules”, each of which comprises a plurality of X-ray detectors. Most modern CT-scanners are multi-slice CT-scanners designed to simultaneously image a plurality of slices of a patient. The X-ray detectors in each CT detector-module of a multi-slice scanner are arranged in a rectangular matrix of rows and columns. The X-ray detector matrices of any two CT detector-modules in a CT-scanner are substantially identical and comprise a same number of rows of detectors and a same number of columns of detectors. The modules are positioned one adjacent to and contiguous with the other in a closely packed array with their rows of detectors aligned end to end so that the X-ray detectors form a plurality of long parallel rows of X-ray detectors. The X-ray detectors in each long row of detectors lie on an arc of a circle having its center located substantially at a focal point of the CT-scanner's X-ray source.
A multi-slice scanner can theoretically be operated to simultaneously image a number of slices of a patient up to a maximum number of slices equal to the number of rows of detectors. However, typically, signals from detectors in a multi-slice scanner are combined in accordance with any of various algorithms known in the art to simultaneously image a plurality of slices that is less than the number of rows of detectors. Methods of combining signals from CT detector-modules are described in U.S. Pat. Nos. 5,241,576 and 5,430,784 and PCT publication WO 98/05980, the disclosures of which are incorporated herein by reference.
A prior art multi-slice CT-scanner may, by way of example, comprise 42 CT detector-modules each comprising 8 rows and 16 columns of X-ray detectors. The multi-slice CT-scanner would then have 8 rows of 672 X-ray detectors. Typically, in operation signals from X-ray detectors in two adjacent rows of detectors may be combined so that the CT-scanner normally operates to simultaneously image four slices of a patient.
Electronic components used to process signals from the X-ray detectors in a detector module are generally sensitive to radiation and if exposed to X-rays at intensities measured by the detectors are quickly damaged to an extent that causes them to become non-functional. As a result, electronic components for processing signals from the X-ray detectors in a CT detector-module are usually located at positions removed from the detector module for which intensities of X-rays from the X-ray source are relatively low. In addition, the electronic components are shielded by appropriate radiation shielding. Each detector in a detector module is connected to the module's electronic processing components via a cable over which signals from the detector are transmitted to the processing electronics.
To an extent to which CT detector-modules in a CT-scanner comprise a greater plurality of X-ray detectors and sizes of the detectors decrease, resolution of the scanner can be increased and flexibility in configuring the CT-scanner for different imaging demands is improved. However, as the number of X-ray detectors in a CT detector-module increases, a required number of conductors in a cable connecting the detectors to the processing electronics increases. To accommodate an increased number of conductors, size of the cable, and in particular sizes of connectors that couple the cable to the CT detector-module and to the processing unit increase. However, space available in a CT-scanner for a CT detector-module is limited and the immediate neighborhood of each of the CT-modules in a CT-scanner is crowded. As a result it does not appear feasible to provide required data transmission capacity using conventional cable for CT detector-modules comprising a number of X-ray detectors substantially larger than a number of X-ray detectors typically comprised in prior art CT detector-modules.
A possible alternative to transmitting X-ray detector signals via cable to processing electronics is to locate the electronics in close proximity to the detectors and connect the detectors to the electronics using electrical connections formed using known microfabrication techniques. The processing electronics might, for example, be located on a same substrate as the detectors and/or on a different substrate connected to the detector substrate using microconnectors known in the art. Known microfabrication materials and techniques can provide, in restricted space available in a multi-slice CT-scanner, connectivity between processing circuits and X-ray detectors in the CT-scanner for a substantially greater number of X-ray detectors than can be provided for by cable.
However, it may not have appeared feasible to locate processing electronics for a CT detector-module in close proximity to the module's X-ray detectors. The X-ray detectors in a CT detector-module are densely packed and are closely coupled to a relatively large anti-scattering collimator. The CT detector-modules in a CT-scanner are also, as noted above, closely packed one to the other and neighborhoods of the detector modules are crowded. As a result, it may have appeared in prior art that insufficient space in the neighborhood of the X-ray detectors of a CT detector-module is available to install radiation shielding sufficient to protect radiation sensitive electronic components located in close proximity to the detectors.